Conventional practice for the generation of electron beams for linear accelerators, free electron lasers, and gyrotrons utilizes thermionic cathodes, or pulsed "cold cathode" sources such as plasma cathodes and field emitters. However, thermionic cathodes are limited in current density, require heater power, radiate heat, and are susceptible to poisoning; and pulsed high voltage diodes emit higher currents but they operate for only a few microseconds at most, and at low duty cycle. Grid control of the conventional sources is also difficult since the grid must operate at the high voltage of the cathode.
Accordingly, a principal object of the present invention is to provide a high density electron beam without the many problems normally associated with thermionic cathodes.